The v-raf murine sarcoma viral oncogene homolog B1, also known as NS7; BRAF1; RAFB1; B-RAF1; FLJ95109; MGC126806; MGC138284; or BRAF, (as used herein, “BRAF”), is a serine/threonine protein kinase that plays a critical role in the MAP Kinase/ERK signaling pathway which mediates physiological cell functions such as growth and differentiation. Aberrant activation of MAP Kinase/ERK signaling can result in the development and progression of multiple types of cancer. As such, the components of the MAP Kinase/ERK signaling pathway are considered attractive therapeutic targets for cancer treatment. In particular, activating mutations in BRAF have been shown to occur in ˜80% of melanoma, ˜50% of papillary thyroid cancer, and 10% of colon cancers with an overall occurrence in ˜8% in all types of cancer. SEQ ID NO 1 displays the full length mRNA Homo sapiens BRAF mRNA and is from Genebank accession number NM_004333.4. In BRAF, the single nucleotide substitution at nucleotide position 1798 (T→A, thymine to adenine) produces an amino acid substitution at amino acid position 600 (V→E, valine to glutamate) in the catalytic kinase domain resulting in constitutive activation of BRAF (as used herein “V600E” or “BRAF(V600E)”). The V600E mutation accounts for ˜90% of all activating BRAF mutations.
Given the importance of activated BRAF and, in particular, BRAFV600E in cancer progression, there has been much effort to develop both pan-RAF and selective BRAF inhibitors as potential therapeutics; multiple agents are currently undergoing clinical evaluation including GSK218436, ARQ 736, PLX3603, PLX4032 (also known as vemurafenib, RG7204 or RO5185426 and herein referred to as “PLX4032”), BMS908662, RAF265, XL281, and BAY 43-9006. Clinical results have shown that tumors harboring activating BRAF mutations show remarkable response, including delay in progression and/or tumor regression, to treatment with such pan-RAF and selective BRAF inhibitors. Despite the initial response to such treatment, the majority of the patients develop resistance to treatment with such pan-RAF and/or BRAF inhibitors within 2-18 months. Preliminary in vitro and animal model experiments have suggested that such acquired resistance can arise from activating mutations in the MAP Kinase/ERK signaling pathway upstream RAS or downstream MEK and from activation of parallel signaling pathways. However, it is still not clear if all cases of resistance are mediated by such mechanisms nor is it clear if such mechanisms are clinically relevant. To date, no compensatory mutations in BRAF itself have been shown to drive said resistance.
Therefore there is a need in the art for further evaluating the mechanism of acquired resistance and to validate such mechanisms in the clinical setting. This will allow more complete diagnostic tests to be developed in order to stratify patients for treatment and will provide an opportunity to better tailor treatment strategies in the resistant patient. Further, there is a need in the art for novel second-line therapeutics to treat patients who become resistant to treatment with pan-RAF and/or BRAF inhibitor(s) and exhibit progression or relapse despite an initial response to BRAF inhibition.